Crystal structure of novel hydrides in a Mg-Ni-H system prepared under an ultra high pressure

The crystal structure of novel hydrides in the Mg-Ni-H system has been studied using a powder X-ray diffraction and transmission electron microscopy. A cubic-anvil-type apparatus was utilized to prepare samples. The new hydride with a chemical composition of around MgH2-60 at% Ni was synthesized at 1073 K for 2 h under a pressure as high as 5 GPa. From TGA analysis, the new hydride was found to be Mg2Ni3H3.4. Orthorhombic and monoclinic crystal systems with a primitive cell were proposed as possible symmetries of the new hydride. X-ray and electron diffraction patterns of the new hydride were indexed in an orthorhombic structure with a=0.8859(4), b=1.3740(5), c=0.4694(2) nm. Moreover, decomposition of the hydride into Mg2Ni was observed by the transmission electron microscopy. (C) 2002 Elsevier Science B.V. All rights reserved.